The in-cluster-sender should properly wait and report state of sender job

[cardil]

Currently, the code fails to wait until a sender job completely fails or manage to succeed in a retry.

https://github.com/knative-sandbox/kn-plugin-event/blob/6d85cfd3588b76bebb2a05b5d345c4eb4a468e21/pkg/k8s/jobrunner.go#L76-L83

Instead, the code should wait for the configured number of retries, and report failures of retries concisely.

Only in case of complete failure, a final error should be produced as described in #129.

/kind bug

[mgencur]

Also, when the job actually fails, the error string is repeated multiple times. This output comes from using the plugin from kn client when the job fails:

Error: can't sent event: can't send with ICS sender: the ICS job runner has failed: the ICS job runner has failed: the ICS job runner has failed: expected to have successful job

[github-actions]

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